What property of the eye is the principle of motion, pictures?

20 Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer. 21 What are the common defects of vision that can be corrected by the use of suitable eyeglasses or spectacles? 23 What are coaxial lenses and where are they used? 24 Draw a diagram of a simple microscope.